With the advent of recombinant DNA technology and the consequent availability of pure probes for the RNA products of specific genes, attention has been focused on the development of convenient and reliable methods for employing these probes to measure the concentrations of specific RNAs in animal cells or organs during induction by hormones, differentiation, etc. Techniques have been described for employing recombinant probes for solution hybridization measurements of absolute concentrations of the corresponding mRNA products of induced genes [Roop, D. R., et al (1978) Cell 15, 671-685; Beach L. R., and Palmiter, R. D. (1981) Proc. Nat'l. Acad. Sci. U.S.A. 78, 2110-2114]. However, for many investigations, measurements of relative mRNA concentrations (experimental/control) can yield the requisite information. Present techniques for this measurement involve either end-labeling of purified RNA with .sup.32 P, followed by hybridization to an unlabeled immobilized recombinant plasmid (Williams, J. G. et al. (1979) Cell 17, 903-913), or hybridization of a .sup.32 P-labeled recombinant plasmid to unlabeled purified RNA which has been either dotted directly to nitrocellulose or transferred to nitrocellulose following gel electrophoresis (Thomas, P. S. (1980) Proc. Nat'l. Acad. Sci. U.S.A. 77, 5201-5205; Dobner, P. R., et al. (1981) Proc. Nat'l. Acad. Sci. U.S.A. 78, 2230-2234).
Analysis of specific mRNA levels by any of these techniques requires that RNA first be isolated, usually by phenol extraction, from a large sample of the cells or tissue under investigation. However, many studies of regulation of specific gene expression, as for example replicate determinations of the time course or dose-response curves of a hormonal induction, require analysis of specific mRNA levels in numerous samples. Purification of RNA from samples of cells and tissues can be a difficult and time-consuming process, involving multiple phenol extractions, precipitation, recovery, and gel electrophoresis prior to analysis. (See for example, Penman, S. J. Mol. Biol. 17, 117 (1966). Brandsma et al., PNAS, U.S.A., 77, 6851 (1980) try whole animal cells dotted to nitrocellulose to detect EBV (Epstein--Barr Virus) but this method yields variable signals in replicate samples i.e. reproducibility is poor. Therefore, the Brandsma method is unsuited for quantitative analysis. Thus, it would be desirable to have available a technique for the simultaneous analysis of relative levels of an mRNA species in multiple samples, which requires both minimum amounts of sample such as of cells or tissue and minimal manipulation of each sample prior to analysis. For many types of regulation experiments, multiple sample analyses are involved.